Over a period of years, engineers and designers of internal combustion engines, including diesel engines, have provided increasingly improved designs of engine cylinders, pistons and piston rings leading to relatively trouble-free operation over greatly extended operating periods. Improvements in operating life have, however, been offset to some extent by repeated increases in engine specific power wherein greater and greater operating loads have been placed upon new designs of engine cylinders and pistons without increasing their size. As a result, the operating conditions under which cylinders, pistons and piston rings are required to operate have become increasingly severe.
It has been recognized that one limitation on the load carrying and wear resisting capabilities of engine piston rings has been the tendency under certain operating conditions to breakage of the ring, particularly the top ring, usually with resultant damage to the cylinder and piston assembly requiring replacement of these parts. Some causes of such breakage have been found and cured. However, a long-standing problem of this sort, existing in two-stroke cycle diesel engines having ported cylinders and a plurality of compression piston rings, has, until now, defied solution by engine designers and contributed to limiting the potential wear-life and specific power capability of engine cylinder assemblies.